The use of silicon as a substrate for integrated circuits and other high technology electronics is well known and has been an acceptable manufacturing material for many years. Specifically, it is well known that silicon lends itself to plasma etching and deposition processes as well as many other well known application techniques which are useful and necessary for the manufacture of miniaturized electronic circuitry. Further, it is also well known that although silicon is capable of operating in elevated temperature environments, it also happens that the performance of a silicon device is significantly degraded at elevated temperatures. For example, to name but a few, it is known that at elevated temperatures silicon will exhibit lower mobility, lower transconductance, higher power consumption, lower threshold voltage, higher junction leakage current and higher metal line resistance. In turn, these problems lead to excess power consumption, degradation of logic levels in electronic components, and degraded noise margin. Further, at elevated temperatures, silicon is also susceptible to what is commonly referred to in the industry as "cross-talk" (i.e. interference that is caused by energy from one signal invading another circuit by electrostatic or electromagnetic coupling). Obviously, the problems set forth above that are directly associated with operation in elevated temperature environments are to be avoided. This is so due to the fact many environments are susceptible to elevated temperatures and need to be effectively monitored. Damage control in ships, aircraft, trains and buildings is a prime example of the need for such monitoring.
It is known that many of the problems which are associated with electronic/chemical/biological sensors can either be minimized or entirely eliminated, if a proper substrate is chosen. The selection of a proper substrate material, however, requires more than the ability of the substrate to tolerate high temperatures. Clearly, many materials which have excellent tolerance of elevated temperatures do not have the other qualities which are necessary for their use as a substrate for electronic circuits. As indicated above, despite recognized shortcomings, silicon has very good operating characteristics and, as also indicated above, silicon is a material which has been widely used in the fabrication of many different electronic circuitry devices. With all of the above in mind, it has been recognized that silicon can still be used, and its susceptibility to diminished performance at elevated temperatures can be minimized, by mounting sensors and their associated electronic circuitry on very thin layers of silicon. Specifically, recent processes have been developed which allow for the fabrication of nearly pure silicon layers that are on the order of only about one thousand to two thousand angstroms in thickness.
In light of the above it is an object of the present invention to provide a microsensor with associated electronics for identifying changes in the magnitude of an environmental characteristic (e.g. temperature, gas concentration, and pressure) when the temperature of the environment is up to as high as in a range of three hundred to five hundred degrees centigrade. Another object of the present invention is to provide a microsensor with associated electronics which will accurately interpret changes in environmental characteristics that occur at elevated temperatures. It is another object of the present invention to provide a microsensor for identifying a change in an environmental characteristic which can do so with minimal power loss, minimal current leakage and minimal cross-talk. Still another object of the present invention is to provide a high temperature active microsensor which incorporates electronic circuitry that can be manufactured using standard manufacturing processes. Another object of the present invention is to provide a microsensor for identifying a change in an environmental characteristic at a temperature up to approximately three or five hundred degrees Centigrade which is simple to use, relatively easy to manufacture, and comparatively cost effective.